Semiconductor processing involves forming Metal Oxide Semiconductor (MOS) transistors on wafers. A MOS transistor typically includes a gate dielectric and a gate electrode, a source and a drain, and a channel region between the source and the drain. In Complimentary Metal Oxide Semiconductor (CMOS) technology, transistors may typically be of two types: Negative Channel Metal Oxide Semiconductor (NMOS) and Positive Channel Metal Oxide Semiconductor (PMOS) transistors. The transistors and other devices may be interconnected to form integrated circuits (ICs) which perform numerous useful functions.
Dielectric materials have important roles in semiconductor processing. In the front end formation of MOS transistors on wafers, dielectrics are used to isolate gate electrodes, among other uses. In this regard, spacer dielectric is applied to the side surfaces of gate electrodes. Such front end gate spacers tend to be composed of silicon dioxide or silicon nitride. However, there materials can have a high dielectric constant (k), can be nontrivial to remove if desired, and, if deposited by PECVD, the conformality of these materials is also subject to a pattern loading effect. Moderate k dielectric also finds use in back end processing, for example as etch stop, hard mask or dielectric barrier layers.